1. Field of the Invention
The present invention relates to an optical card, and, particularly, to a cardlike information recording carrier for optically recording and reproducing information.
2. Related Background Art
Recent years, as the society becomes progressively informationized, various information recording carriers and apparatus for optically recording and reproducing information, including an optical disc, an optical card, an optical tape, etc., have been proposed as a means for dealing with a great variety of information with high efficiency. Such information recording carriers include those which can detect the binary-coded information by a change of reflectivity a change of strength of reflected light which accompanies with a change of surface shape corresponding to the presence or absence of pits(holes), or a change of polarized light surface by magnetooptic effect. These information recording carriers are characterized by having advantages such that they can achieve high recording density and can perform non-contact recording and reproducing, and therefore can enjoy a long life.
Studies and development have been also extensively made in recent years in respect of cardlike information recording carriers (hereinafter referred to as optical cards) having good portability and having a large capacity considering their size.
The information recording carriers for optically recording and reproducing information will be described below by making reference to the optical cards.
Referring to how to optically record and reproduce information, there is performed, for example, the magneto-optical recording in which the magnetizing direction is reversed by an energy beam, the recording performed by forming concavo-convex pits, or the recording by utilizing the difference in optical reflectance. Usually, however, widely used are recording carriers utilizing the difference in the optical reflectivity as they have a high S/N ratio and can be easily produced.
As the recording carriers utilizing the difference in optical reflectivity, there have been proposed, for example, cards having a recording layer comprising silver particles dispersed in a gelatin matrix. The writing of information in this recording layer is carried out by irradiating a laser beam on the recording layer to form recording pits.
On the other hand, there have been proposed the so-called heat mode recording elements, in which recording is carried out by irradiating an energy beam such as a laser beam on a recording layer in the form of a spot and changing in part the state of the recording layer. As these recording layers, used are metallic thin films comprising tellurium, bismuth, etc., organic thin films comprising polystyrene, nitrocellulose, etc., dye thin films comprising cyanines, or tellurium low oxidized product films utilizing phase transition. These recording elements do not require any development processing or the like after writing of information, and are called DRAW (direct read after write) media that can "read immediately after writing", by which high density recording can be performed and additional writing can be also performed.
FIG. 3 is a plan view showing a recording format of a conventional DRAW type optical card.
In FIG. 3, an optical card 1 which is the recording carrier is provided on it with a recording area 2, and the recording area 2 is formed by a track 3 arranged in plurality. In the track 3, further formed are a start bit and a stop bit, and the track 3 has information capacity of about several thousand bits. Each of the track 3 is also partitioned by a reference line 5 (hereinafter "R-line"). Arrow A indicates the direction in which the optical card 1 moves at the time of reproducing.
FIG. 4 is a schematical view of an optical card reproducing process.
In FIG. 4, the optical card 1 is movable in the direction of arrow A by means of a rotating mechanism 6. The information recorded on the optical card 1 is read by an optical head 11 for each track 3 and reproduced. First, light from a light source 7 such as a semiconductor laser is condensed by a lens system 8, and irradiates the track 3 on which the information has been recorded. An image of the track 3 irradiated is formed on a sensor 10 through means of an image formation optical system 9, and an electrical signal corresponding to the information recorded on the above track 3 is output from the sensor 10.
Once the read-out on the above track 3 is completed, the optical card moves in the direction of arrow A or the optical head 11 moves in the direction in which the tracks 3 are arranged (the direction of arrow C), so that the information on the subsequent track 3 is read in the similar manner.
To gain access to an arbitrary track 3 on the optical card 1, the optical head 11 is moved in the direction of arrow C. The optical head 11 counts the R-line 5 to select a track 3 to which a target track 3 intended to be read belongs, and stops when reaches the target track 3. Subsequently, the optical card 1 is moved in the direction of arrow A by means of the rotating mechanism 6 to perform read-out of information on the target track 3.
In this manner, in the conventional information recording carrier such as the optical card 1, information can be optically read or reproduced by utilizing the light irradiated from the light source 7 provided on the optical head of the optical recording and reproducing apparatus.
As described above, in carrying out the reproducing on the optical card, the optical card 1, while tracking is performed, moves in the direction of arrow A by means of the rotating mechanism 6 to perform the read-out of information, but occasionally the optical card stops because the optical card may reversingly move along with its move in the direction A, during which the writing may proceed, though very slowly, owing to the energy of read-out light, until it turns difficult to detect the tracking signal. In other words, the energy of the read-out light repeatedly irradiates a portion of the optical card when movement is stopped, and this irradiation may alter the optical characteristics of that portion of the card.